A bisected mold being vertically bisected along an equatorial plane of a tire and a sectional mold being split into multiple pieces in a circumferential direction of a tire, which pieces are expanded and contracted with respect to a center, have heretofore been known as molds used for vulcanization molding of an unvulcanized tire.
The bisected mold has an advantage of capabilities to simplify and reduce a size of mold equipment. On the contrary, in the case of a tire having a complicated tread pattern in recent years, problems may occur including: a large resistance at the time when a tire is separated from the mold; a manufacturing defect that the mold is opened with the tire being attached firmly to an inner surface of the mold; and a failure such as cracks.
Meanwhile, the sectional mold, which is split into multiple tread segment units in the circumferential direction of a tire, can deal with a complicated tread pattern. On the contrary, there is a problem of causing an increase in mold costs because it is necessary to provide a complicated sliding mechanism separately.
Accordingly, molds for vulcanization molding of a tire having a structure of a combination of a bisected mold and a sectional mold have been disclosed (see Patent Documents 1 and 2, for example).
Nevertheless, such a mold for vulcanization molding of a tire employs a structure in which multiple split segments are configured to expand and contract with respect to the center along with opening and closing actions of a top shell and a bottom shell obtained by vertically bisecting the mold. An elastic force of a spring is utilized for the mold's opening and closing operations of the segments. For this reason, there has been a problem of pinching an unvulcanized tire and causing a manufacturing defect of a tire because the segments' action of uniformly tightening the tire is not stabilized at the mold clamping in particular.
Patent Document 1: Japanese patent publication No. 3608161
Patent Document 2: Japanese patent application Kokai publication No. 2000-127173